The present invention relates to a method of forming a para-dielectric and ferro-dielectric capacitors over a silicon substrate.
Dielectric films are used as a capacitive insulation film for capacitor in a semiconductor device. A dynamic random access memory has a plurality of pairs of a transistor and a capacitor. The capacitor has a capacitive insulation film which may be either a para-dielectric film or a ferro-dielectric film. The ferro-dielectric film used provides the capacitor with a non-volatile function. The para-dielectric film is essential for processing analog signals. In the above circumstances, it is required to locally and selectively form the para-dielectric film and the ferro-dielectric film over a single silicon substrate.
A conventional method of forming the para-dielectric film and the ferro-dielectric film over a single silicon substrate locally and selectively over a single silicon substrate will be described with reference to FIGS. 1A through 1D.
With reference to FIG. 1A, a silicon oxide film 52 is entirely formed on a silicon substrate 51. A conductive film is also entirely formed on the silicon oxide film 52. The conductive film is patterned by a photolithography and subsequent dry etching process thereby to form first and second bottom electrodes 53A and 53B on different regions of the silicon oxide film 52. A first dielectric film 54 is entirely deposited, which extends over the first and second bottom electrodes 53A and 53B and the silicon oxide film 52. The first dielectric film 54 may be deposited by either a sputtering method or a chemical vapor deposition method. A first top electrode 55 is selectively formed on the first dielectric film 54 over the first bottom electrode 53A.
With reference to FIG. 1B, the first dielectric film 54 is selectively etched by use of the first top electrode 55 as a mask so that the first dielectric film 54 remains only under the first top electrode 55 and over the first bottom electrode 53A. The remaining part of the first dielectric film 54 serves as a capacitive insulation film for a first capacitor which comprises laminations of the first bottom electrode 53A, the first dielectric film 54 and the first top electrode 55.
With reference to FIG. 2C, a second dielectric film 56 is entirely formed, which extends over the first top electrode 55, the second bottom electrode 53B and the silicon oxide film 52. A second top electrode 57 is selectively formed on the second dielectric film 56 over the second bottom electrode 53B.
With reference to FIG. 2D, the second dielectric film 56 is selectively etched by use of the second top electrode 57 as a mask so that the second dielectric film 56 remains only under the second top electrode 57 and over the second bottom electrode 53B. The remaining part of the second dielectric film 56 serves as a second capacitive insulation film for a second capacitor which comprises laminations of the second bottom electrode 53B, the second dielectric film 56 and the second top electrode 57.
As described above, the first capacitive insulation film in the first capacitor may be different in dielectric substance from the second capacitive insulation film in the second capacitor. If, for example, the first capacitive insulation film is a para-dielectric film and the second capacitive insulation film is a ferro-dielectric film, then the first capacitor serves as a capacitor for processing analog signals and the second capacitor has a non-volatile function to serve as a memory capacitor. The above conventional method has the following three problems.
The first problem is concerned with an increased number of processes for manufacturing different kinds of capacitors. Namely, the different kinds of capacitors are separately formed in different fabrication processes. This results in an increased time for manufacturing the capacitors.
The second problem is concerned with limitation to available methods of forming the layers for the second capacitor. When the second capacitor is formed, the step has already been formed, for which reason it is difficult to use the methods sensitive to the steps such as the sol-gel method.
The third problem is concerned with that variation in property or characteristic of the first dielectric film is caused when the second capacitor is formed. If, for example, the first dielectric film is formed at a temperature of 400.degree. C. and the second dielectric film is formed at a temperature of 600.degree. C. this means that the first dielectric film already formed is heated at the higher temperature of 600.degree. C. when the second dielectric film is formed. As a result, the first dielectric film varies in structure and constitutional elements of the first dielectric film may be diffused into exterior whereby the characteristic is changed.
In the above circumstances, it has been required to develop a novel method of forming different kinds of capacitors locally and selectively over a single silicon substrate with no change in characteristic and nor increase in the number of fabrication processes.